This invention relates to pressurizing of a closed-type container and more particularly to technique for injecting gas under pressure into a closed-type cylinder having a piston rod slidably and sealingly projecting through one end of the cylinder such as a hydropneumatic shock adsorber or a gas spring.
It is known to pressurize a closed-type cylinder such as a hydropneumatic shock absorber by forming a small hole or an orifice in the wall of the cylinder, supplying gas under pressure to the interior of the cylinder through the orifice, and closing the orifice permanently by welding or the like with or without utilizing a closure member such as a plug inserted into the orifice, as shown in, for example, British patent specification No. 996,356 and U.S. Pat. No. 3,081,587. But such prior art methods have shortcomings; for example it is troublesome and expensive to form the gas filling orifice in the wall of the cylinder and to plug the orifice and to perform a welding operation around the periphery of the plug to assure sealing of the cylinder, and the welding equipment for such an operation is complicated. Further, it is impossible to adjust the gas pressure after the gas filling and sealing operation has been performed.
According to another prior art method for filling a closed-type cylinder such as a hydropneumatic shock absorber with gas, there is provided a seal member between a cap member closing one end of the cylinder and either a rod projecting from the cylinder or the inner wall of the cylinder in sliding sealing engagement, and the seal member is adapted to deform or displaced inwardly so as to form a passage therearound, so that high pressure gas applied on the outside of said one end of the cylinder can enter the cylinder. But since the seal member displaces or deforms according to the differential pressure generated across the seal member, it has been difficult to obtain the desired pressure in the cylinder.